The reason is because (in the absence of clairvoyance) the performance of stocks is evaluated over time. If the price is closer to $45 in a month or two, it'll be easier to say that today's price jump was an aberration. If the price is $180 in three months, it'll be possible to say that today's price is actually too low.
But we aren't discussing the long-term performance of the stock here - we are discussing the wide range between what their initial offer is, and the amount the IPO underwriters got to take home.
